Bridge wire



Patented. May 11, 1937 I UNITED STATES BRIDGE WIRE Bert Brenner, Union, N. 1., assignor to Sigmun Cohn, New York, N. Y.

' No Drawing. Application September 11, 1936,

- Serial No. 101,269

3 Claims. (01. 75-172) This invention relates to improvements in bridge wire for blasting cap resistance units or any resistance wire used to set 011 explosives, and has for its object the provision of a new alloy for 5 such devices which is stronger and cheaper than such as have been available heretofore.

The most eifective alloy for resistance units for electrically operated blasting caps has been, until now, made of twenty percent (20%) irid- 10 ium and eighty percent (80%) platinum. A wire made of this alloy possesses the desirable property of resisting corrosion, is fairly strong,

chemically homogeneous and constant in its electrical characteristics.

iii qualities it came to be generally used in spite of the fact that it is quite costly.

I have discovered that an alloy of rhodium, ruthenium and platinum possesses all of the desirable characteristics of the iridium-platinum 20 alloy formerly used and that it has several important features of advantage over it. For example, a wire made of an alloy of fifteen percent (15%) rhodium, five percent (5%) ruthenium and eighty percent (80%) platinum, has about 25 one hundred percent (100%) higher tensile strength than one made of the aforesaid iridiumplatinum alloy of the same diameter. By reason of the lower specific gravity and lower specific resistance it is also possible to use a thinner wire 30 for a given resistance and still have this wire stronger mechanically, say of fifty percent (50%) more tensile strength than said platinum-iridium wire of the same resistance.

The specific gravity and specific resistance of 35 my new alloy are less than that of the iridiumplatinum alloy, so that there is greater length in a given weight. These facts together enable the purchaser to obtain anincrease of approxi mately thirty percent (30%) in length of wire per unit of weight at 'a certain resistance. This is important as it is usually-sold by weight.

As the market price for rhodium and ruthenium is generally only about half that of iridium, in 45 addition to the above advantage of greater length per unit weight there is a considerable saving in price. The intrinsic values of my alloy and twenty percent (20%) iridium-platinum are now about $59.00 and $72.00, respectively. This rep-- resents a saving of about eighteen percent (18%) which, added to the thirty percent (30%) saving described above and due to the more favorable specific gravity and specific resistance, makes a total saving figured on a dollar basis of forty- 55 eight percent (48%). These prices may fluctu- Because of these desirable ate. They indicate, however, an approximate proportion.

Pt-Rh- Ru alloy Pt-Iialloy Percent Percent I sa s Ruthenium The temperature coefiicient of electrical resistance-of this alloyis about forty percent (40%) lower than that of the aforesaid platinum-iridium alloy. This is an added advantage since the change in resistance is less than with the platinum-iridium alloy in the temperatures surrounding blasting operations, which may be between 50 F. to +150 F.

The particular alloy described is typical of a series of alloys consisting of various proportions of rhodium, ruthenium and platinum, all having similar characteristics and advantages. I have found that the practical limits within which the proportion of the three metals may be varied are:

Rhodium 2-25% Ruthenium 2-15% Platinum Balance alloys:

Platinum 15 Rh- Ru Melting point C... 1330 Specific gravity Resistance per mil foot at 20 Temperature coeflicient of resistance per C. (0-100 C.) Ultimate tensile strength (herd) pounds per square inch Elongation percent (hard) Approximate length In feet per ounce per 100 ohms per foot at 20 C The following table is a comparison of the two tions of 2% to 25% rhodium, 2% to 15% ruthenium, and the balance platinum.

2. An alloy for resistance units comprising rhodium, ruthenium and platinum in the propor- 5 tions of 15% rhodium, 5% ruthenium and 80% platinum.

3. An alloy for resistance units substantially composed of rhodium, ruthenium and platinum in the proportions of 2% to 25% rhodium, 2% to 15% ruthenium, and 60% to 96% platinum, having the characteristics herein described, including high tensile strength and low temperature 00- emcient of resistance.

BERT BRENNER. 

